Or, to quote Scorpions:
So give her inches and feed her well, more days to come, new places to go, I've got to leave, it's time for a show
I don't exactly think they were talking engines, but, you can pretend they were.
300hp 307
- Thread starter MadDrOlds
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So give her inches and feed her well, more days to come, new places to go, I've got to leave, it's time for a show
I don't exactly think they were talking engines, but, you can pretend they were.
The 307 is simply built as a low RPM torque utility motor. Its why the Qjets for Olds 307s lack idle air bypass, a feature needed for higher flowing engines. Its was designed for the era of 55 speed limits. Its much much easier to get 300 emission legal HP out of a Chevy 305 than a Olds 307.
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To the list of "good" parts listed above, add a Set of ARP studs for the mains and heads, plus a set of ARP Bolts for the rods. Lose the stock oil pump in favor of a Hi flow pump with better gears or wider ones. This isn't about pressure it is about feed and volume. To the cam, add a good timing chain and matching gears.
Pull the candidate down to nuts and bolts and hot tank it. Do the standard battery of checks and inspections to the block, and then check the cylinder bores for round and use a torque plate when doing the final bore/hone. At the very least lose the stock cast pistons in favor of a set of hypereutectic ones. Not as strong as forgings but better for the street than the OEM castings. Not sure if going the blueprint route would gain you much but it would give you some peace of mind to know all the internal specs are within parameters.
Nick
Pull the candidate down to nuts and bolts and hot tank it. Do the standard battery of checks and inspections to the block, and then check the cylinder bores for round and use a torque plate when doing the final bore/hone. At the very least lose the stock cast pistons in favor of a set of hypereutectic ones. Not as strong as forgings but better for the street than the OEM castings. Not sure if going the blueprint route would gain you much but it would give you some peace of mind to know all the internal specs are within parameters.
Nick
Are full length headers and dual exhaust allowed? Otherwise, good luck. The Performer RPM intake is a must as well. Also a lot of time porting lousy stock heads and adding 1.87/1.56 valve would be needed. Also the right cam and probably a custom chip to deal with the aggressive timing curve with at least a 1 to 1 compression increase. Definitely possible, 450+HP has been done, just not emissions legal.
One of the biggest problems with these motors besides the windowed mains was the heads had tiny journals and they just don’t breathe, you have to move air to get the horse power as mentioned above. Good news is the 350 and 403 also use a similar block and all of your 307 stuff that you
Might need will bolt right on…. Throw away your 307 heads. Just don’t tell anyone it’s not a 307
Might need will bolt right on…. Throw away your 307 heads. Just don’t tell anyone it’s not a 307
Is there any problem fitting full length headers in, say with a Pypes dual setup? I ask because you made special note of the “full length”
Ok, so lets say you just replaced the heads entirely. Say Performer heads and intake. And lets say you can squeeze 300hp out of it.
Do you really think 300 hp is going to lead to a cracked block?!
Roller engines had the peanut, aka "fun size" ports on the 7A heads. Flat tappet 307s had the "full sized ports" as it were. In any case, 307 heads leave much to be desired whatever their port sizes are. Additionally, 307s and later 350s used 1/2" head bolts where 76 and earlier 350s use 7/16". So there's that. You'd be limited to 77 and later 350 heads unless you're going head drilling. TBH, I don't mess with Frankenblocks like that so I haven't done that much research on it. Additionally, 307 #5A 307 heads are very similar to early 350s in combustion chamber size (around 65cc), but later 350 head chambers are huge and would drop compression ratio considerably. #7A 307 heads are totally useless if you want to make serious power. But if you're going to try and use 350 heads, you might as well use the 350 block, too. 🙂
Sorry to piss on the parade, but the biggest issue is going to be keeping it emissions legal as you imply in the OP. Which means YOU CANNOT USE DUAL EXHAUST. So good luck with that. No 307 Olds engine I'm aware of ever came with true dual exhaust, thus in order to keep it technically EPA legal, you have to run those street-legal headers into one cat. Then it doesn't matter what happens after the cat. Just passing an emission test isn't the only qualifying factor for keeping it legal. You can't simply half-azz it. It either meets EPA standards or it does not. Maybe if you get a fat azz cat with 3" exhaust. I don't know. It can be done. Factory 4th gen LS1 Camaro Z28s and SSs ran two cats into a single pipe to the muffler then dualed out from there (a la 79-80 Hurst and 442 style) and their stock rating was 310 HP. My stock 2002 SS with SLP Blackwing intake filter and CME muffler/tails dynoed out at 326 RWHP with just a few thousand miles on it. So it's possible, but a stretch with a 307.
I don't think Edelbrock makes a head that will work with the tiny 3.80 bore of a 307
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